1. Field of the Invention
This invention relates to a disc turbine rotor assembly equipped with at least one labyrinth seal whose concentric sealing rings interdigitate with a corresponding features of a labyrinth seal mounted in the sidewall of the rotor housing, and affordances which assist in assembly alignment and inspection, positional verification, and which provide access to working fluid in the immediate vicinity of the labyrinth seal for sensing or sampling.
2. Description of the Related Art
Turbines comprised of spaced-apart rotor discs were first described by Nikola Tesla in U.S. Pat. No. 1,061,142 and 1,061,206. For this reason, these turbines are sometimes referred to as Tesla turbines, but are alternatively known as Prandtl layer turbines, boundary layer turbines, cohesion-type turbines, and bladeless turbines.
The turbine rotor consists of a stack of discs spaced apart and fixed to a rotatable shaft. The rotor assembly is contained in a housing closely fitted to the perimeter of the discs. The discs have vents near the center, and the housing includes at least one outlet near the center. In operation, an energetic fluid at pressure and temperature is introduced at the periphery of the disc stack and contained in a housing which closely follows the perimeter of the discs. The fluid passes between the discs and exits the stack assembly through vents near the center, leaving the housing through its outlets.
The tangential flow component of the working fluid creates centripetal force within the working fluid, which must be overcome by additional fluid entering the housing. Therefore, in the steady state, a significant drop in pressure exists between the inlet and the outlet of the machine.
For a turbine that introduces working fluid at the periphery of the rotor assembly and exhausts said fluid axially through outlets near the center, any portion of the working fluid allowed to circumvent the rim of an end disc will traverse the outward facing surface of the end disc and escape through the outlet, and will impart significantly less momentum to the turbine rotor than the fluid which enters between a pair of discs and departs though the disc vents.
It is therefore understood that flow of working fluid across the outward facing surface of an end disc represents a loss of mechanical efficiency, and that methods and devices which impede fluid flow along this route are desirable and useful, and represent advances in the state of the art.
Several prior art solutions, including Burgess (U.S. Pat. No. 6,000,701) for example, employ rubbing or wiping components which physically close the gap between the stationary turbine housing and the rotating surfaces of the end disc or of the shaft. However, physical contact increases rotational friction, impedes starting, and introduces maintenance and wear issues and their concomitant costs of operation.
Other solutions, such as Ackermann (U.S. Pat. No. 4,218,066) require that a set of abrasive surfaces on one part are assembled so that they tear close-fitting running grooves into comparatively cancellous or friable material. This method unfortunately generates foreign matter such as material chips or swarf, which must be removed or contained by some additional sealing stratagem. A relative alignment shift of the complimentary sides of the seal releases more foreign matter; should this occur while the turbine is running, said foreign matter may diffuse into the working fluid and be carried off and deposited at unwanted locations.
Tesla in U.S. Pat. No. 1,329,559 discloses a device which impedes fluid flow by means of a series of labyrinthine passages which turn the fluid flow back on itself. In this device, violent eddies are produced which substantially impede fluid flow in an unwanted direction.
A disadvantage inherent in the prior art is that following final assembly of a turbine rotor in its housing it becomes difficult to assess whether the rotational components contained in the inner chamber of the housing are properly centered. One prior art method of eliminating concentricity errors consists of turning the end rotor and rotor seal glands out of a single mass of material. The disadvantages of this method include increased machining time required to make such a part, and a significant increase in material waste driven by the larger volume of material which must first be secured and then removed. Both of these factors detrimentally increase the cost of such a part.
Experimentation has shown, and commonly published tables of discharge coefficients show, that abrupt squared-off passages, sharp edges, and abrupt changes of flow cross sections also sharply reduce fluid flow. For the purposes of this specification, the term xe2x80x9cre-entrant cornerxe2x80x9d shall be used to define an edge interface between two surfaces that meet at a dihedral angle. The inventive labyrinth seal impedes fluid flow across the outside face of an end disc by forcing the fluid through a sequence of sharp-edged features and squared-off or re-entrant corners which effect abrupt changes in fluid direction and sectional flow areas, as well as abrupt and turbulent changes in momentum, velocity and pressure in the fluid attempting to pass through the seal. The second law of thermodynamics reveals that such changes of fluid state waste internal energy. Such dissipation of internal energy is a source of resistance to fluid flow.
The inventive labyrinth seal complicates the flow pattern by varying the dimensions of adjacent portions of the passage defined between the seal elements such that passage portions having a small sectional flow area are followed by passages with a greater sectional flow area. Empirical formulae commonly applied in the science of fluid friction to find fluid energy loss parameters such as the Darcy friction factor, relate frictional loss to the square of the flow sectional area. Under this relation, in choosing between an area reduction of 5% and of 10% for example, marginal analysis shows that the first 5% of area reduction will effect a 9.75% loss effect, while the second 5% will effect an additional loss effect of only 9.25%, with continually diminishing effect for further degrees of flow sectional area reduction. Thus, a sequence of sectional flow area differences can be arranged to produce any desired energy loss or impedance.
A labyrinth seal in accordance with the present invention has features on a rotating component that must be correctly aligned with complimentary features on a stationary component in order to operate properly. The inventive labyrinth seal includes inspection ports through the housing to ascertain the proper assembly position and optimal adjustment during the final stages of assembly. The labyrinth seal also provides both adjustable and centralizing features that coaxially align all salient features of the rotating components to a first axis, and align all salient features of the stationary housing components to a second axis.
Run-out and other errors of concentricity are inherent in any object containing features desired to be concentric. Means of adjustment permit an assembly strategy capable of counteracting the accumulation of radial dimensional and radial positional errors in manufacture. It is also advantageous to afford adjustment to assembly concentricity and axial position with the least degree of required disassembly. This is accomplished by means of a plurality of inspection ports through which gages can be inserted to align the seal members to the housing during assembly. A plurality of countersunk fastener openings in the housing receive complementary fasteners which can be tightened while the seal member is aligned by the gages. The fastener openings are enlarged relative to the fastener shank to permit movement of the seal member relative to its mounting surface.
Working fluid is accessible from a point substantially upstream from the final exit of the fluid past the innermost gland and into the exhaust through one or more of the inspection ports. The working fluid so sampled represents an intermediate condition between the thermodynamic states of the fluid at inlet and exhaust. The thermodynamic state of such sampled matter will vary in similarity with the state of inaccessible working fluid within the turbine itself. Measurements of its state and variations thereof can provide a useful means of investigating and controlling the operation of the mechanical system of which the turbine is a part. As an example, an automatic control system may include variations of pressure and temperature measured at this access point as disturbance inputs in an algorithm used to control a combustion process upstream of the turbine, in order to secure a system providing controllable power output and predictable fuel consumption.
An object of the present invention is to provide a new and improved labyrinth seal for a disc turbine that improves turbine efficiency by impeding in a manner free of rotational friction, the flow of working fluid seeking to escape across an outward-facing surface of an end disc.
Another object of the present invention is to provide a new and improved labyrinth seal for a disc turbine that permits inspection of the installed position of the components of the labyrinth seal from outside the disc turbine housing.
A further object of the present invention is to provide a new and improved labyrinth seal for a disc turbine that compensates for cumulative dimensional variations, or tolerance stack up to maintain the concentricity of the assembled components of the labyrinth seal.
A yet further object of the invention is to provide a new and improved labyrinth seal having means for adjusting at least some components during a final assembly stage, so that radial dimensional and radial positional errors in manufacture and assembly can be minimized.
Finally, an object of this invention is to provide access to working fluid in the immediate vicinity of the labyrinth seal for sensing or sampling.